1. Field of the Invention
The present invention relates to an ink-jet recording method excellent in reliability and capable of giving a high image density. The present invention is appropriately applicable to a recorder (recording apparatus), in particular, one needed for a high image density on a light transmissible substrate for diagnosis in the medical field and for a reference picture, or the like.
2. Related Background Art
The ink-jet recording method is for the purpose of making a record by ejecting small ink drops and sticking ink to a recording medium such as paper. In particular, according to an ink-jet recording method disclosed in Japanese Patent Publication Nos. 61-59911, 61-59912 and 61-59914, or an ink-jet recording method in a process to generate liquid drops by using an electrothermal converter as ejecting energy supply means to give thermal energy to ink and create bubbles, making a recording head into high-density multi-orifices can easily be implemented and an image of a high resolution and high grade can be recorded at high speed.
As coloring materials in ink employed for the ink-jet recording method, water-soluble dyes are principally used. When printed on a light transmissible substrate at a high density, however, such water-soluble dyes exhibit a high transparency. Thus, an application to a high image density required field has a problem of having difficulties in yielding a maximum image density in comparison with an image density obtained by a wet silver salt process.
To overcome a problem related to water-soluble dyes as mentioned above, using a highly hiding coloring material such as dyes is considered. However, if a pigment, in particular carbon black, is employed as coloring material to obtain a high image density, another problem takes place that the so-called bottom color of the pigment is marked at the highlight part, the color tone becomes reddish meaning a high value of b* in CIE (L*a*b*) and no clean graded expression is obtained. Incidentally, here, CIE is an abbreviation of Comission Internationale de l""Eclairage.
Made to solve the above problems in the background art, the present invention takes a purpose in providing an ink-jet recording method capable of implementing a high transparent image density and a great maximum image density, a good tone and an excellent gradation.
The present invention for solving the problems is an ink-jet recording method by using a multiple sorts of black ink different in concentration to make a graded record, characterized in that a first type of ink employed for the above graded recording and a second type of ink containing a different coloring material from that of the first type and further increasing the maximum density expressible with the first type of ink on a light transmissible recording medium.
Besides, the present invention provides an ink-jet recorder for making a graded record by using multiple sorts of black ink, comprising first ink attaching means for attaching a first type of ink used for the above graded recording on a transmissible recording medium and second ink attaching means for attaching a second type of ink containing a different coloring material from that of the first type and further increasing the maximum density expressible with the first type of ink on a transmissible recording medium.
An ink-jet recording method and an ink-jet recorder according to the present invention are especially effective for the application to a transparent recording medium such as recording medium for the OHP.
Hereinafter, the background leading to the present invention will be described. First of all, when attaching ink to a transparent recording medium for the OHP, even when attaching ink containing a dye as coloring material to a recording medium for the OHP multiple times, there was difficulty with an increase in optical density (OD) and the density after a value of OD reaches about 2.5 could not be raised. Then, an attempt to use ink containing a pigment as coloring material instead of the dye ink succeeded in raising a value of OD up to about 3.5, but it was found that the hue was tinged with red brown in a relatively low density portion of an image and the image grade was not favorable.
Thus, it was found that on coloring portions other than the maximum density portion in the image with a dye ink and coloring the maximum density portion with a pigment ink capable of raising a value of OD higher than the dye ink, the problem of hue in portions other than the maximum density portion is solved and the OD value can be sufficiently raised at the maximum density portion, thus resulting in perfection of the present invention.
Besides, it was found to be attributable to a higher light scattering of pigment ink than that of dye ink that whereas use of dye ink could not raise a value of OD above a predetermined value, use of pigment ink could raise a value of OD still higher.
Like this, according to the present invention, a combined use of ink containing coloring materials different in light scattering for the grade recording on a recording medium enables a high grade image excellent both in hue and density to be obtained in the case of coloring a recording medium, especially a transparent recording medium.